Thanks all for the pragmatic advice. @hifihandyman problem is I don’t want to be connecting and disconnecting my source all the time - cable termination wear and tear paranoia on expensive gear and cables etc…
Mola Mola also got back to me and said it should be okay, provided impedances are compatible and that I only ever use the Manuka volume knob and leave the headphone amp set to 0.
But this seems less than ideal and they did say the output from the Makua wouldn’t be typical for the input of the headphone amp, so I’d wonder what effect that might have on sound. Looks like I either need to give up my Mola Mola Makua with embedded Tambaqui for a preamp with a tape/line out, or I need to settling for a new and secondary source chain for my future headphone amp, which won’t be anywhere near as high end as what I have in my main system. Seems like the more practical option is to replace the Makua and Tambaqui, problem is I love the sound of both and I don’t want to seperate the DAC from the preamp.
Still in the early planning phase of setting my direction for my headphone setup so this gives me a leading direction to explore. Thanks all.